The ever increasing demand for clean energy that is alternative to the conventional fossil-fuel based power generation has been one of the primary driving forces for the recent development of photovoltaic (PV) technologies, especially in the past decade. The majority of new installations of PV generation systems is grid interactive and enjoyed a 70% increase of capacity worldwide in 2008. The power electronic converter is an indispensable subsystem that interfaces the PV modules with electric power systems.
As indicated by a rich body of literature records, various new topologies of PV inverters have been proposed and studied. Nonetheless, previous studies suggest that the PV inverter still remains the weak link in PV power generation systems with regard to its reliability. The lifetime of PV inverters is approximately 5-10 years as opposed to the 30-year lifetime of PV panels. The relatively short lifetime of inverters not only increases the effective operating cost, but also poses a significant stress on the environment in light of life cycle analysis, which contradicts one of the primary motivations of developing renewable energy generation, namely to relieve the stress to the environment imposed by the energy production processes.
The key issues related to PV inverters that negatively affect the reliability performance include the electrolytic capacitor, which commonly exists in PV inverters using the dominant topology of voltage source inverters (VSIs). The less frequently researched current source inverters (CSIs) could potentially eliminate the electrolytic capacitor while providing additional benefits. The adoption of CSI in PV systems, however, is significantly limited by the availability of suitable power semiconductor devices. Three-phase CSI have also been proposed for application in PV generation systems. Thus far, the single-phase topology is predominant for residential systems with capacity below 10 kW peak power.
For single phase dc/ac inverter systems, with no regard to either VSI or CSI topology, the pulsating nature of the instantaneous power flow is in common. The pulsating power flow will manifest itself in the form of either dc-link current ripple or voltage ripple in a single-phase CSI or VSI, respectively. The low-frequency ripple on the dc-link will potentially have adverse consequences. Therefore, it is desirable to develop an improved topology for a power inverter that minimizes the low frequency ripple.
This section provides background information related to the present disclosure which is not necessarily prior art.